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Tektronix TDS744 CRT to LCD color converter FPGA module DIY

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ltarjanyi75:
Hello Terry,

Good to hear, that your solution finally works. Did you manage somehow to solder the LED/diode to the same board you made the photo of before, or did you designe another board?

I have a Spartan 6 and it also does not contain clamp diodes. Unfortunately I have not checked it before and I designed my "plug in board" like yours for my Spartan 6 devboard with only serial resistors. And of course it is already in production... :(
Now I'm thinking how I would replace the resistors for the LED/Diode combo at the same place, without redesigning and producing a modified PCB.
Btw, would the LED/diode combo work for all signals? Why it is only important for data lines and clock? (because of 3-state data lines and importance of clear clock?)

TerrySt:
Yes, I managed to add the led/diode to my existing board.  It wasn't easy, and it isn't pretty, but it let me test it.  I did it only on the data and clock lines because it was so difficult to do that I didn't want to do it on all the lines.  It is most important on the data lines because they are not just high/low.  They also go tri-state.  This left the inputs to the level shifter ICs floating, which is bad because it causes high currents in the IC and even oscillations.  This was causing a lot of noise on my board.  I also wanted to remove the clock from the level converter IC since there was noise from the other signals on that IC getting coupled into the clock.  Changing just the data and clock signals reduced the clock jitter enough to allow the PLL in the Spartan to give a good phase locked 175MHz clock for the lvds lcd.
I did a re-spin of the pcb which will use the led/diodes on all of the lines.  The parts I used are very small:
LED:  DigiKey p/n 732-12015-1 (0603 package)
Schottky diode:  DigiKey 641-1784 (SOD523 package)
You need good eyes (I have a microscope) and patience to solder them by hand.

Another way that would work for your case is to use your series resistor but add the schottky diodes from the input of the FPGA to the 3.3V supply.  That should work, but will slow the rise/fall times to the signals slightly depending on the resistor value.  The value is a trade-off between speed and how how current is drawn from the signal lines when the diode conducts.  I the case of 330 Ohm resistors, that would be (5v - 3.3v - 0.2v)/330 = 4.5mA.
The led/diode method doesn't slow the signals and doesn't draw any extra current from the signal lines.

Terry

TerrySt:
The lcd looks great.  The colors and contrast look really good to me.  It is hard to take a picture that looks as good as it does live.  I've just got it taped in place in the scope and still have the protective plastic cover on the screen so the reflections are bad in the photo.  I will make a mounting bezel for it and try to find some sort of anti-reflective plastic or glass protection cover for it.
This is the G065VN01 V2.  The backlight brightness is set to about 50%, which seems plenty bright.

Tantratron:
All my congratulations Terry, bravo.

Regarding the intensity control, namely the selected Waveform % with the selected text % and how your FPGA code generating the PWM duty cycle for LED back light signal, how did you set the specifoc algorithm fusing each % request ?

Albert

ltarjanyi75:
I agree with Albert, nice work Terry! The LCD screen looks great!

If I'm not mistaken, the brightness can be set by the dip switches on the board.

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